Portable circuit interrupter tester and method

ABSTRACT

A portable circuit interrupter shutoff testing device and method, including a high current switch controlled by a timing circuit that allows current to flow through the switch and a small series resistance (in order to trip the instantaneous-trip function of the interrupter, as opposed to the overload-trip) for a short time period relative to the sine wave of the electrical power. A button activates the timing circuit which in turn activates the switch and current flows limited by the internal resistor of the device. By limiting the on time of the device to one or a few half cycles, the user can test if the circuit interrupter responds as quickly as specified by the manufacturer. A method includes receiving a stimulation indication, and selectively connecting an electrical load to wires connected to the circuit interrupter, wherein the electrical load is sufficient to trigger the instantaneous-trip function of the circuit-interrupter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application U.S. patentapplication Ser. No. 10/293,524, filed Nov. 12, 2002; which claimsbenefit of U.S. Provisional Patent Application No. 60/337,650, filedNov. 13, 2001; each which is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

This invention relates to electrical circuitry testers, includingcircuit-interrupter testers. More particularly, it relates to the methodand apparatus for testing and breaking instantaneous circuitinterrupters in electrical boxes and outlets.

BACKGROUND OF THE INVENTION

Instantaneous circuit interrupters (also called instantaneous circuitbreakers) and overload circuit interrupters (also called overloadcircuit breakers) are important components used to protect electricalcircuits. Often, an instantaneous circuit interrupter and an overloadcircuit interrupter are packaged in a single device simply called acircuit breaker. Typically, a plurality of suchcombination-circuit-breaker devices are installed in a “breaker box” or“panel” used to protect a corresponding number of electrical circuits ina house or building.

Instantaneous circuit interrupters supply a means of interruptingcurrent that might be dangerous to people or the wiring circuit, as inthe case of a short-circuit overcurrent that could result in a fire orelectrocution. An instantaneous circuit interrupter typically employs anelectromagnet switch to open immediately (with no intentional timedelay) when a high multiple of the rated current is sensed. On the otherhand, an overload circuit interrupter typically employs a bimetal stripswitch to open after a slight delay (with an intentional time delay thatis inversely proportional to the amount of overcurrent) when a lowmultiple of the rated current is sensed. A third type of circuitprotection interrupter, called a GFCI (Ground Fault Current Interrupter,also known as GFI) interrupt current being drained off a circuit toground that could present a shock hazard to people. Often a combinationof an instantaneous circuit interrupter, an overload circuit interrupterdevice and a GFCI device are incorporated serially in the same circuitor combined into a single unit.

There are three basic situations where circuit interrupters come intoplay and open the circuit. First when there is a short circuit causing asudden very high surge of current. This should trip the instantaneouscircuit interrupter. Second when there is an ongoing load that drawsmore current than the interrupter is rated for. This should trip theoverload circuit interrupter. Third, when there is some current beingdrawn off to ground. This should trip the GFCI.

In each of these situations there are very definite specifications as tohow long the interrupter has to respond. It is essential that thesedevices operate within these parameters, either to open quickly as in ashort circuit or an improper ground, or relatively slowly as in the caseof a smaller overload. For instance in the latter situation where, whena motor is starting up, the motor may draw a much higher current for ashort period of time. It would be inconvenient to have the breakertripping at these times. Thus, circuit breakers have an overload circuitinterrupter employing a thermal element that allows small overcurrentsfor limited time periods. But in the case of a short circuit or a groundfault it is essential that the breaker interrupt the current flow asquickly as possible, generally within a few cycles of AC power.

Each of these sensing capabilities can function independently of eachother. For instance, a short circuit can trip a circuit breaker (i.e.,the instantaneous circuit interrupter) in a panel while the GFCIupstream of it is unaffected. Similarly, an extended overcurrent cancause the thermal portion of a circuit breaker to unlatch while the GFCIremains unaffected. Finally, a GFCI can trip while the circuit breakerdownstream remains in the closed position. The capability of tripping asquickly as possible is called the instantaneous tripping response.

Conventional circuit breaker testing devices suffer by only testingeither circuit breakers or GFIs. Ideally one device should be able totest either selectively and separately.

Devices heretofore known suffer from one or more of the followingdisadvantages:

(a) the circuit breaker is not predictably tripped;

(b) a part of the device is consumed in use, as with an internal fuseblowing;

(c) requiring the user to travel back and forth between the circuitbreaker panel and the point in the circuit where one wishes to work;

(d) switching off and on of multiple circuit breakers, which will affectappliances on those circuits;

(e) requiring two devices, a transmitter and a receiver;

(f) removal of the breaker from the panel;

(g) does not switch off the breaker from the location where one wishesto work;

(h) tests and trips a GFI device but not the circuit breaker protectingthat GFI device;

(i) tests the thermal sensor of the circuit interrupter as opposed tothe instantaneous magnetic tripping capability of the interrupter;

(j) overstresses the circuit by drawing more wattage (volts times amps)or power (volts times amps times time) than actually required for such atest;

(k) cannot be used at any point in the circuit of the circuit breaker;

(l) potential damage to wiring and the device in the event of thecircuit breaker not tripping off;

(m) excessive heat being dissipated during the time it normally takesthe breaker to trip;

(n) damage to switch contacts due to arcing;

(o) tests either only a circuit breaker or a GFCI, but not eitherselectively (this means two separate devices are required instead ofone);

(p) does not test if the circuit interrupter is operating withinprescribed specifications, but only if it functions at all;

(q) does not incorporate an interrupter within the device that willrespond to various dangerous situations such as the device's switchfusing closed while there is a load of sufficient magnitude to presentan overheating condition in the wiring of the circuit or in the deviceitself;

(r) incorporates an interrupter within the device that may blow duringnormal operation of the device's testing procedure;

(s) incorporates an interrupter within the device that will not respondto a load of sufficient magnitude to prevent an overheating condition inthe wiring of the circuit or in the device itself; and/or

(t) contains a fuse that may blow during testing that is within theinterrupter's specified operating range (for instance, an 800-ampcurrent for ½ cycle of AC power) or would not respond in a potentiallydangerous situation (for instance, a 40-amp overload of extendedduration on a 20-amp circuit).

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides an instantaneous circuitinterrupter tester that:

(a) can be used to test circuit breakers to see if they respond properlyto an overload or short (circuit breakers can become faulty over aperiod of time from aging of inner spring elements or from corrosion dueto influences such as moisture and humidity);

(b) will work predictably, efficiently and repeatedly without damage tothe device;

(c) will not require the user to visit the breaker panel;

(d) will not require switching off breakers other than the one inquestion;

(e) is presented in a single package;

(f) works without removal of the breaker from the panel;

(g) will trip the breaker from the location where one wishes to work;

(h) will not trip the GFI while testing or tripping the circuit breaker(regardless of whether it is a GFI circuit breaker or not);

(i) will test the instantaneous tripping capability of the interrupterwithout causing the thermal sensor portion of the interrupter to trip;

(j) will dissipate a minimum amount of heat;

(k) can be used at any contact point in the circuit without damaging thedevice of the present invention;

(l) will not present a danger in the event of the interruptermalfunctioning;

(m) will operate for a relatively short period of time resulting in lesstotal wattage being drawn through the circuit;

(n) will have a switching device that is not subject to arcing damage;

(o) will selectively and separately test different types ofinstantaneous circuit interrupters;

(p) will test that a circuit interrupter's interrupting capability isequal to or greater than the interrupter's actual specifications; and/or

(q) (r) (s) will incorporate an interrupter within the device that willallow loads of required magnitude during normal testing without opening,while opening the circuit within the device in situations where thedevice misbehaves, such as if the switching element fused closed while acircuit breaker does not open. For instance, if the switching devicefused shut, but the impedance of the circuit was high enough to preventa load of sufficient magnitude to trip the breaker or if the breaker wasmalfunctioning, then one could have the potential situation of alarge-enough current being drawn to overheat the wiring or the devicethus presenting a fire hazard.

Further, in the case of testing circuit breakers, my invention is notpolarity sensitive, meaning that it will function correctly even if theneutral and charged wires, to which it is connected, are reversed.

Additionally, in some embodiments, my invention provides a light toindicate if the circuit is energized or not and/or a light to showwhether the load resistor has blown.

Another feature is the incorporation of one or more means of turning offthe current through the device in case of a faulty circuit breaker inthe existing circuit.

A further embodiment of the present invention has the initial testperformed concomitantly with a measurement of the amperage of that test.If the amperage is below a predetermined measure, then the resistor isswitched out of the circuit and the test can be repeated with either asmaller value resistor or no resistor at all.

This invention of this disclosure deals with both the safety and effortissues by providing a simple, inexpensive, portable device that bothtests an instantaneous circuit interrupter and turns off the power fromthe location where the person wishes to work. The power is effortlesslyturned off and thus the circuit breaker to that outlet is instantlylocated and identified.

It is the intention of this disclosure to put into possession of thepublic means for designing and building a remote control circuitinterrupter test device with optimum characteristics of accuracy,effectiveness, durability and safety.

It is interesting to note that, while in the process of developing thedevice of the present disclosure, I have been told by electricalengineers and manufacturers that the SCR will burn out, that the loadresistor will burn out, that there isn't enough power in the electricalsystem to allow the device to work, that such a large current surge willprevent the timing circuitry from working reliably, that it will causefires in the wiring of the circuit breaker and so on. They say either itwon't work, or if it does work, that it will fail during testing or ifit works once, it won't work again if the breaker doesn't trip. Inactual use the device does work, as expressed, for instance, in that itdoes trip circuit breakers that are operating within specifications in awiring circuit at is up to code. It also works in that when presentedwith a breaker that will not trip, one can repeat the test repeatedly.And the prototypes tested simply haven't burned out. It is believed thatat least part of this is the lack of understanding about electricity'scharacteristics during fractions of a second. For instance, a circuitbreaker that “sees” a single half cycle of 60-Hz electricity “feels” amagnetic field that can trip it, yet the total current, and thus heatgenerated, is much less than is generally realized. An ampere is a unitof charge per second. A certain number of electrons moving per second.When one 120th of a second is viewed, the current is one 120th of theamperes that some people suppose is in action. Additionally, a materialthat is rated in watts, such as a 50-watt resistor, is utilizing ameasurement of amperes time volts. Thus watts is a time dependent unitof measure. Since the wattage of a resistor is a measurement of theamount of heat generated that it can withstand, and that heat is createdover time, there can be dramatically different performance when the timethe resistor is exposed to the current is extremely short. By analogy, aperson will burn their finger if it is held over a flame, but if thesame person moves the same finger through the same flame quickly, thereis no damage to their skin. A measurement of the temperature of theflame may indicate that the finger should have been burned, but inactual practice it is not. Having pointed this out, it may now seemobvious, but this aspect of electricity's effects being time dependanthas not been applied to circuit breaker testers before the device of thepresent disclosure.

An instantaneous circuit interrupter tester is provided by a deviceincluding a high current switch controlled by a timing circuit thatallows current to flow through the switch and a series resistance for atime period and in units relative to the sine wave of the circuit towhich the device is connected. The user connects the device to thecircuit of the circuit interrupter by means of, for instance, prongsthat mate with a wall outlet. An indicator, such as a light or meter,indicates whether there is power to the outlet. Pressing a buttonactivates the timing circuit, which in turn activates the switch andcurrent flows limited by the internal resistor of the device. Bylimiting the on time of the device to multiples of half cycles the usercan test if the circuit interrupter is actually capable of responding asspecified by the manufacturer. Further, by limiting the test to suchshort periods, the circuit interrupter and its associated circuit wiringand receptacles are subject to a minimum of stress.

It is a feature of this device that it can be used to test circuitbreakers or ground fault interrupters. The only adaptation requirementsbeing which contacts in the outlet are used and the size of theresistance element. Dual resistances and a switch can make a singledevice capable of selectively testing either type of interrupter.

The present invention provides a simple and effective way to test theinstantaneous-trip function of a circuit-interrupter. One aspect of theinvention provides a tester for a circuit-interrupter, wherein thecircuit-interrupter includes an overload-trip function and aninstantaneous-trip function. This tester includes an electrical plughaving a first external electrical connector and a second externalelectrical connector, a control circuit that outputs a control signal,an electronic switch selectively enabled by the control signal, and anelectrical load connected to the electronic switch such that theelectronic switch connects the electrical load to the first externalelectrical connector and the second external electrical connector ascontrolled by the control signal, wherein the electrical load issufficient to trigger the instantaneous-trip function of thecircuit-interrupter.

In some embodiments, the control signal enables the electronic switch toconduct limited to a time no greater than a pre-specified maximum triptime of the instantaneous-trip function. In some embodiments, thepre-specified maximum trip time of the instantaneous-trip function isthree cycles of AC power. In some embodiments, the electronic switch isenabled to conduct for a time no greater than about one-half cycle of ACpower.

Some embodiments further include a ground fault tester circuit thatcomprises a small current load selectively coupled between the firstexternal electrical connector of the plug and a third externalelectrical connector of the plug.

Another aspect of the present invention provides a method of testing acircuit-interrupter, wherein the circuit-interrupter includes anoverload-trip function and an instantaneous-trip function. This methodincludes receiving a manual stimulation indication, and selectivelyconnecting an electrical load to wires connected to the circuitinterrupter based on the reception of the manual stimulation indication,wherein the electrical load is sufficient to trigger theinstantaneous-trip function of the circuit-interrupter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a simplified schematic of tester circuit 100 of oneembodiment of the invention.

FIG. 1B shows a simplified schematic of tester circuit 101 of oneembodiment of the invention.

FIG. 1C shows a simplified schematic of tester circuit 102 of oneembodiment of the invention.

FIG. 1D shows a simplified schematic of tester circuit 103 of oneembodiment of the invention.

FIG. 1E shows a simplified schematic of tester circuit 104 of oneembodiment of the invention.

FIG. 1F shows a simplified schematic of tester circuit 105 of oneembodiment of the invention.

FIG. 2A is a perspective view of a circuit breaker interrupter/tester200 embodying features of the present invention.

FIG. 2B is a perspective view of a circuit breaker interrupter/tester201 embodying features of the present invention.

FIG. 3 shows the relative positions of the device of this disclosure andthe elements of the existing electrical system.

FIG. 4 is a log-log graph of tripping time vs. current of a sample90-amp circuit breaker.

FIG. 5 is a graph showing several complete cycles of AC electricity withnormal load current and current during an overload.

FIG. 6 is a graph 600 displaying variations in amplitude of an ACelectrical sine wave subsequent to turn on.

FIG. 7 is a log-log graph of tripping time in seconds verses multiplesof current rating of a circuit breaker.

FIG. 8 is a log-log graph of tripping time in seconds verses multiplesof current rating.

FIG. 9 is a circuit diagram of one embodiment of the device.

FIG. 10 is a wiring diagram of another embodiment of the device.

FIG. 11 is a circuit diagram of the device of FIG. 10.

FIG. 12 is a flow chart showing the operation of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which are shown by way of illustration specific embodiments inwhich the invention may be practiced. It is understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

The leading digit(s) of reference numbers appearing in the Figuresgenerally corresponds to the Figure number in which that component isfirst introduced, such that the same reference number is used throughoutto refer to an identical component that appears in multiple Figures.Signals and connections may be referred to by the same reference numberor label, and the actual meaning will be clear from its use in thecontext of the description.

Another further embodiment of the present invention includes multipleselectable load circuits, for example, by having a switch that selectsfrom a plurality of values for load resistor 120. Thus one could performtests of either low or high current loads, and still be able to limitthe time or number of half cycles during which the excess current isdrawn. This could be accomplished, for instance, by a selector switch toselect between two different parallel loads each in series with a singleSCR switching element. Another method to accomplish this would be tohave two loads, each in series with its own SCR switch and a selectorswitch between the timer and the SCRs. One advantage to the lattermethod is that a smaller switch could be utilized as it would only becarrying the current necessary to turn on the SCRs.

Another further embodiment of the present invention is to have a circuitthat presents a relatively high resistance load (i.e., low amperage)between the hot and ground terminals to test a GFCI.

Another further embodiment of the present invention is to haveswitchable means to perform the same test accessing either the hot andneutral wires or the hot and ground wires. This would be of advantage inaccessing the quality of the ground. Additionally, if the neutral wiredoes not make a good connection but the ground wire does, then thebreaker could still be tested. Obviously it is also possible to connectthe hot wire to both the neutral and ground wires simultaneously.

U.S. Pat. No. 2,976,484 (McClain Mar. 21, 1961) is a circuit fuselocator. It is basically a device with a plug leading to two parallelcircuits, one of which has a pilot light and the other has a switch anda fuse. It is plugged into a receptacle leading to a fuse of loweramperage rating than the fuse in the device. By closing the switch thecircuit is shorted resulting in blowing the fuse protecting thereceptacle. In the event of the fuse protecting the receptacle beingrated larger than the fuse in the device, the fuse in the device willblow, protecting the circuit and the switch. I have built and testedthis device and it works as claimed with fuses and fuse panels. However,it does not work effectively and predictably with circuit breakers. Inexperiments with a receptacle leading to a circuit breaker, the devicewill usually both trip the breaker and blow the fuse in the device.Sometimes the fuse in the device will blow, but leave the circuitbreaker unaffected. Either way the fuse in the device would usually haveto be replaced with each usage on a circuit protected by a circuitbreaker. Thus although this device is a circuit fuse locator, it was notintended to be nor can it be considered a circuit breaker locator.

One might think that it would be obvious to simply remove the fuse inthe device, but no one has advanced such an idea since U.S. Pat. No.2,976,484 was issued. The obvious reason is that if you have no fuse inthis device, there are at least two potential deleterious side effects.First, in the case of a faulty circuit breaker that would not trip off,the main limit to the length of time the short circuit would besustained is how long it would take to overheat the wiring and switchand eventually melt one or both of them and thus open the circuit.Second, the switch contacts will wear out due to arcing or overheating.

Another category of device has been invented to identify a singlecircuit breaker among a plurality of circuit breakers that involve sometype of transmitter and a separate receiver. One of these is placed ator near the circuit breaker panel and the other somewhere in the loadside of the circuit of the breakers. The transmitter sends some type ofsignal through the wires, which is sensed by the receiver, thusdetermining which wire or receptacle goes with what breaker.

One such device (Konopka U.S. Pat. No. 4,906,938) is placed in theoutlet that sends a signal to the panel. A detection device held to thepanel senses which circuit is receiving the signal. This requires a tripto the outlet to plug in the transmitter, then to the panel to use thesensor and manually turn off the breaker and back to the outlet to getto work.

Another device connects an electrical noisemaker to an outlet. Then theuser goes to the panel and flips breakers until the noise either ceasesor starts (Peak U.S. Pat. No. 4,725,772 and Peak U.S. Pat. No.4,816,746). This is a variation on the time-honored trial and errorpractice of plugging in a loud radio and then going to the panel andflipping breakers until the radio turns off (or on). Aside from theeffort of going to the panel, which my invention eliminates, the turningoff and on of multiple breakers means any devices on those circuits thatrely on uninterrupted power (such as digital clocks) will have to bereset.

Yet another device requires removal of the breaker and utilizes, amongother components, one or more transformers, coils, relays and avoltmeter to generate and measure the exact amount and duration ofcurrent necessary to flip the breaker (Elder U.S. Pat. No. 3,678,372).Although it is a wonderful testing device, it does not address theproblem of turning off the breaker from the outlet.

U.S. Pat. No. 4,803,434 to Walker describes a tester that connectsdirectly to the breaker in the panel. Although a spectrum of resistancesare incorporated into the testing circuit in order to test either theinstantaneous or thermal breaker elements, no mention is made of anyspecific timing circuitry. It seems to be intended to test specializedcircuit breakers that incorporate three leads and an electronic tripcomponent. The device of the present invention specifically includes atiming means for controlling the length of the test of the circuitbreaker or interrupter whose advantages are described in depth elsewherein this document.

U.S. Pat. No. 3,852,660 to Maier and Shimp also describe a tester thatconnects to a set of special input terminals on a molded circuitbreaker. The device is limited to breakers having such specialterminals. The device of the present invention does not have thislimitation as it is designed to be used anywhere in the circuit of thecircuit breaker to be tested.

U.S. Pat. No. 5,812,352 to Rokita and Davis tests overloads as opposedto short circuits. It places an overload on a circuit breaker, which, insome embodiments, is two times the breaker's rating. For instance, totest a 15-amp circuit, a 4-ohm 500-watt resistor is specified, whichresults in a 30-ampere load. It will be apparent by looking at FIG. 4that such a load is two times the breaker's rating which should resultin the breaker being tripped in between 15 and 100 seconds. Althoughsuch a load should not harm most breakers, the wiring of the circuitbetween the device and the breaker is subjected to considerable heating.Also, Rokita's tester is testing the breaker's bimetallic thermalelement, which responds to the heating effect of the current through thebreaker. It is not a large enough load to test the “instantaneous”magnetic element that responds to the magnetic field produced by currentthrough the breaker. Additionally, the 500-watt resistor is physicallyvery large, which makes the device less convenient to carry about. Also,the process of the current flowing through this resistor will generateconsiderable heat that would have to be dissipated.

U.S. Pat. No. 5,736,861 to Keleher and O'Neal describes a circuitbreaker tester that measures the impedance of the circuit the device isconnected to and then, if the impedance is within specified parameters,which are the safe operating range of the circuit breaker tester, atimer closes a relay that applies a short circuit across the activeline. If the measured impedance is not acceptable, the device will notallow the user to test the circuit. As this device relies on the wiringto supply at least a minimum impedance, if it is used too close to thebreaker there would be insufficient impedance to allow operation. Thussome outlets could not be used as testing points, or if the entirecircuit is too short it could not be tested at all. Further, the timerthat operates the relay is specified as having a duration of from 0.1 to10 seconds. As circuit breakers normally are rated to trip within 3cycles of AC power, or 0.05 second, it is apparent that the actualspecifications of the breaker are not being tested. In other words, itmay test if the breaker works at all, but not if it is functioningwithin actual specified parameters. With their device the breaker couldpass the test when in actual fact it would not trip as intended by themanufacturer. This could lead to a breaker being thought of as safe andthus being kept in service when in actual fact it could lead to ahazardous situation.

Additionally, the extended period of time that the tester is on can leadto excessive heating of the circuit's and the device's components. Whatis desired is a circuit breaker tester that will test the breaker'sactual specifications or perform an even more exacting test. Thus abreaker that passes this test is then known to either meet or exceed themanufacturer's specifications. Additionally it is desirable to have atester that can be implemented at any point in the circuit, regardlessof how near to the circuit breaker. The defining aspects of such atester are twofold, first that the time the load is on is either equalto or less than the rated tripping time, and that the sum total of theimpedance of the circuit and the device be sufficient to be within thesafe operating area of the circuit breaker tester's load switchingdevice while producing a load of sufficient magnitude to meet thetripping requirements of the circuit interrupter. The total stressplaced on the circuit and the tester will be minimized proportionally asthe time the tester is on is shortened. Additionally Rokita's devicerequires doing an impedance measurement before testing the circuitbreaker. The device of the present invention allows testing immediatelyupon connection to the circuit of the circuit interrupter, saving timefor the user.

U.S. Pat. No. 5,736,861 to Keleher and O'Neal (column 2 lines 21 to 27)also describes a circuit breaker tester that includes a fuse specifiedas “a high current, quick blow, 1000-amp rated device.” It furtherstates this fuse “is selected to have a characteristic that will notallow it to blow under the range of conditions normally found in typicalbranch circuits that are shorted for two seconds or less. Such fuses arecommercially available.” In the same column, lines 66 and 67, the ontime of the device is described as “That time is preferably set to avalue between 0.1 to 10 seconds.” Two problems may arise out ofselection of such a fuse as they specify. First, if there is a fault inthe testing device that allows an overcurrent of, for example, 100 amps,the device's fuse will see this as a normal load so this overcurrentcould continue long enough to cause damage to the circuit connected tothe circuit breaker without causing the fuse to blow. If the circuitbreaker of the circuit were to be faulty, there would be little or noprotection at all. Second, the fuse is rated to withstand a shortcircuit for two seconds, but the test, which can allow a very highcurrent, for example, 800 amps, is specified to continue up to 10seconds. Although 800 amps is not the same as a true short circuit, ifthe fuse allows this amount of current to pass in a normal test, itcould cause damage to the circuit of the circuit breaker.

In contrast, what is desired in the present invention is a fuse or otherovercurrent protection device that will allow a short surge of currentbut not allow moderate overcurrents for longer than is safe. Forexample, a fuse that will allow a half-cycle surge of current of 800amps, but open after some safe time length if there is a continuousovercurrent of 40 amps. Happily, the resistor that is used as a load inthe device of the present invention functions in exactly this way. Itcan withstand a half cycle of high amperage current, but will open (bymelting) with a prolonged current, even a relatively small prolongedcurrent. Also, a small gauge wire such as copper or nichrome wire can beincorporated as a fusible link by having it in series with the large SCR1110 and load 120. It is simple to perform tests to select what is thesmallest gauge wire that can be used repeatedly, while still being smallenough to provide circuit protection.

U.S. Pat. No. 5,736,861 to Keleher and O'Neal further describes using arelay switch that is intrinsically incapable of the short time periodsof which the device of the present invention is capable. Relays aremechanical devices that must move physical contacts a distance, whichlimits the speed at which they can switch, and thus cannot close andopen in less than a certain specified minimum time that is much greaterthan that of semiconductor devices. This is a further limitation whenone is trying to have the circuit close at a zero cross moment. Therelay works by building up a magnetic field in a coil that causes thecontacts to move. The time it takes to charge the coil and then move thecontacts makes trying to hit right on a zero-cross moment, or acontrollable point relative to the zero-cross moment difficult orimpossible.

Another class of prior invention that either tests ground faultinterrupter circuit breakers (Strock U.S. Pat. No. 3,898,557 and RocciU.S. Pat. No. 3,984,765) or whether the ground and hot, and neutralwires are correctly installed (Donahue U.S. Pat. No. 3,205,436, SolgereU.S. Pat. No. 3,263,164, Shapiro U.S. Pat. No. 3,668,518 and Spear U.S.Pat. No. 3,952,244). Ground Fault Interrupters (GFIs) turn off a circuitbreaker in an outlet when a leakage of current to the ground isdetected. These GFI testing devices test the connections between the hotand neutral conductors in various ways to verify if the GFI isfunctioning properly. This test does not extend to the circuit breakerat the panel. In other words, the leakage of current to ground may turnoff the GFI breaker, but does not turn off the circuit breaker at thepanel (unless the circuit breaker is a special GFI circuit breaker).Generally these devices produce a simulated ground fault by connectingthe hot and ground contacts via a resistor. A very small current isallowed that is within the GFIs specifications. However, the testgenerally lasts as long as the user holds their finger on the testingswitch. Obviously this does not test if the GFI will, for instance, tripwithin one and a half cycles of AC power, as is a common specificationfor such devices. It would be desirable if the test period was equal toor less than the actual rated tripping time.

One other useful aspect of the device of this disclosure addressestesting nuisance tripping (the high inrush of current during the firsthalf-cycle of applied power, for example, when initially applyingelectrical startup power to a motor). With the load set from between sixand thirteen times the FLA (Full-Load Amps, the amount of current amotor can be expected to draw under full load (torque) conditions whenoperating at the rated voltage), one can test the nuisance trip settingof an instantaneous interrupter. It is essentially the same test asstated elsewhere in this disclosure, except the results are to have thebreaker not trip in a situation which simulates the normal high inrushcurrent of a motor, yet to trip in a situation when this is exceeded.The six to thirteen times multiple of FLA are given here as examples oftypical inrush current multiples of normal and high efficiency electricmotors, respectively. Obviously multiples of LRA (Locked-Rotor Amps, theamount of current the motor can be expected to draw under startingconditions when full voltage is applied) and other electrical ratingscan also be tested. As motors and standards evolve, these can be adaptedto with varied loads and time lengths of testing. Obviously the safeoperating area of the components of the tester must be sizedappropriately to the magnitude of testing current and the time length ofthe test. For example, with a 40-amp-rated motor which may have a seventimes full load current at startup for a half-cycle of AC power multipletests could be run. For instance, one with a seven times FLA for asingle half-cycle, which should not trip the instantaneous interrupter.Secondly, for example, a two-full-cycle test (four half cycles) withseven times the FLA, which should trip the instantaneous breaker. Asnoted elsewhere, although four half-cycles can be used in testing, onecan also test with two half-cycles during two full-cycles (half-cycleon, half-cycle off, half-cycle on, half-cycle off) or two half-cycles onduring one and a half-cycles (half-cycle on, half-cycle off, half-cycleon). Obviously other combinations of current magnitude, testing timelength and on/off patterns of half-cycles can be applied.

Accordingly, the nuisance trip test enables testing of not only at whatmagnitude of current the instantaneous interrupter trips, but also atwhat point in time relative to the AC sine wave. Thus, testing of fixedand adjustable instantaneous trip settings as concerns multiples of FLAis enabled.

FIG. 1A shows a schematic of tester 100 according to one embodiment ofthe invention. Tester 100 includes connection 170 to the circuit of theinstantaneous circuit interrupter, power supply 140 having DC output 141and zero cross connection 142 to the microcontroller 134. In someembodiments, connection 170 includes hot prong 172, neutral prong 171and ground prong 173. Controller circuit 130 includes microcontrollercircuit 134 (used for timing control), optional selector 135 (such asshown in FIG. 1B) to choose length of test period, trigger input 132(e.g., a momentary-contact switch), optional selector switch SW2 136(which, in some embodiments, chooses which test is to be run(instantaneous or GFCI)). Some embodiments include load resistor 120(e.g., resistor/fuse R19), which acts as a high-current load (e.g., 0.15ohms, 50 watts). In some embodiments, this resistor 120 acts as a fusethat opens if a high current is seen for too long a period, such as afailure of SCR 110 that shorts it, or a failure of controller 130 thatturns the SCR 110 on for too long a period of time.

In some embodiments, a switch (such as shown in FIG. 9 as SW4) isprovided in conjunction with load resistor 120 to select from among aplurality of load resistances for load resistor 120. Thus, a resistancecan be selected to test the instantaneous-trip function, or to test theoverload-trip function, or to test that the nuisance-trip function(i.e., that the circuit breaker does not trip as a result of applying aslight overload for a limited period of time, for example, simulating amotor startup procedure).

In some embodiments, a slow-blow fuse or fusible link 179 is provided inseries between hot line in 172 and the internal hot connections 174(which is also used as the low-voltage ground), while other embodimentsomit this fuse. Some embodiments include power indicator/ready-to-useindicator 180 (e.g., LED D5 and an appropriate load resistor R13,connected, for example, to either the power supply as shown in FIG. 1A,or to an output of controller 134 as shown in FIG. 1B). For testing theinstantaneous interrupter function, circuit 100 also includes electronicswitch 110 (in some embodiments, an SCR is used, since a triac may notswitch off as readily). In some embodiments, gating element 150 (In someembodiments, a triac) is included and used to divert a small currentthrough resistor 160 (e.g., R17, in some embodiments, is 20,000 ohms)between hot conductor 172 and ground conductor 173. Some embodimentsfurther include a switch (not shown) to tie ground and neutraltogether).

The electronic switching elements 190 thus can include a tester for oneor more of GFCI function, short (instantaneous-trip) function, and/oroverload (thermal-trip function). In each case, tester 100-105 includesone or more controllers 130 that stop conduction of the respectivetrip-testing function at a predetermined point in time that is relatedto the specified trip time of the circuit interrupter being tested.

For example, for testing an instantaneous-trip function of circuitinterrupter that specifies that it is to trip within 1/20 of a second (3full cycles of 60 Hz AC), the switching element 110 conducts for a halfcycle in some embodiments (in other embodiments, two, three, four, five,or six half cycles of conduction are used). In some embodiments,non-consecutive half cycles are used.

For another example, for testing a GFCI-trip function of circuitinterrupter that specifies that it is to trip within 1/20 of a second (3full cycles of 60 Hz AC), the switching element 110 conducts for threeconsecutive half cycles in some embodiments (in other embodiments, onetwo, four, five, or six half cycles of conduction are used). In someembodiments, non-consecutive half cycles are used.

For yet another example (see FIG. 1F), for testing an overload-tripfunction of circuit interrupter that specifies that it is to trip within100 seconds (6000 full cycles of 60 Hz AC), the switching element 111conducts for 12,000 consecutive half cycles in some embodiments (inother embodiments, other numbers of half cycles of conduction are used).In some embodiments, non-consecutive half cycles are used.

Some embodiments also include GFCI tester that includes triac 150 and alow current/high resistance (e.g., about 5.5 milliamps/about 20K ohm)resistor 160. Switch 136 can be switched so that the gate pulse outputgoes to the gate of triac 150 (instead of to SCR 110) to test the GFCIfunction by diverting about five mA to the ground, thus creating animbalance between the current in the hot conductor and the current inthe neutral conductor. In some embodiments, triac 150 is triggered ineach of three consecutive half cycles (e.g., negative going, positivegoing, and negative going). In other embodiments, other numbers of halfcycles and other patterns of triggers are used (e.g., four consecutivepositive-going half cycles, without conducting during the interveningnegative half cycles). In other embodiments, an SCR is used in place oftriac 150.

FIG. 1B shows a simplified schematic of another embodiment 101 of theinvention. This circuit is substantially identical to that of FIG. 1A,except, in this embodiment, resistor 120 is moved to the closestconnection to the hot terminal, in order that most failures or shortswithin circuit 101 would cause resistor 120 to open (i.e., act as afuse). FIG. 9 shows a complete circuit 900 that represents oneembodiment of tester 101 of the invention shown in FIG. 1B.

In a device 100 or 101 as described above, the manual action needed toactivate control circuit 130 is pressing push button switch 132.

In other embodiments, e.g., circuit 102 as shown in FIG. 1C, controllercircuit 130 omits switch 132, and instead controller circuit 130provides an initial delay after power is supplied (e.g., about tenseconds in some embodiments; but other embodiments use other delaytimes, such as about one second, about two seconds, about five seconds,about twenty seconds, about 40 seconds, or any other suitable timeperiod (generally, a human-perceptible time period, in order that theuser will see the light 180 being on and then turning off)), and thenprovides one or more pulses to turn on SCR 110. Eliminating this switch132 can reduce cost, increase reliability, and obviates the need forpushing the button at the device, thus allowing the user to plug in thedevice at an outlet remote from the breaker panel, then go to thebreaker panel and switch on the circuit breaker being tested to seewhether the circuit breaker is tripped at the set delay time (e.g., tenseconds after power is applied). This can provide additional safety, inthat the user plugs the tester device into an inactive circuit, and,since power is applied by the user at the panel, the user can manuallyswitch off the breaker if it does not get triggered in the appropriateamount of time (perhaps replacing it with another breaker).

Thus, the manual action used to trigger circuit 100-105 could be justplugging the device (102 or 103) into an active circuit and waiting thedelay period, or plugging the device (102 or 103) into an inactivecircuit, then activating the circuit breaker being tested and waitingthe delay period (e.g., 10 seconds) to see that it tripped as it wassupposed to.

In some embodiments (either circuit 104 with switch 132 as in FIG. 1E orcircuit 103 without switch 132 as in FIG. 1D, but otherwise as describedabove), controller circuit 130 omits switch 136, triac 150 and resistor160, thus omitting the GFCI testing function, and simply providing theinstantaneous trip-testing function of SCR 110.

In some embodiments such as shown in FIG. 1F, (either with or withoutthe GFCI testing function) an additional SCR 111 (like 110) and resistor121 (like 120, but of a higher resistance (e.g., 3 ohms, and thus lowercurrent of less than ten times the rated current) are provided, andanother trigger is provided by switch 133, thus providing a test of thethermal-trip (i.e., an overload equal to a low multiple of the ratedcurrent of the circuit breaker 338 (see FIG. 3)) function of the circuitbreaker being tested. In such embodiments, controller 130 provides alarger number of pulses to this additional SCR 111 (perhaps 6000 pulsesto obtain 100 seconds of overload, in some embodiments).

For the above embodiments, resistor 120 is about 0.15 ohms, which limitsthe short-circuit current to about (110 volts to 120 volts)/0.15 ohms,which equals about 733 to 800 amperes. Some embodiments will omit thecurrent-limiting resistor 120, and instead will count on the internalresistance of the electronic switch 110 (or will incorporate aresistance into switch 110) along with the resistance of the wiring 320(see below) to limit the current during the half cycle of switch 110being activated. In some embodiments, a ground-fault-circuit-interrupter(GFCI)-type circuit breaker 327 (such as can be installed in an ordinaryoutlet box) is included in series with wires 320 and outlet 326.

FIG. 2A is a perspective view of an outlet-plug-type circuit breakerinterrupter/tester 200 embodying features of the present invention. Insome embodiments, the instantaneous circuit breaker tester 200 includesone of the variations of circuit 100-105 or 900, and is illustrated inseveral Figures of the drawings and is designated therein by the generalreference character 200. Tester 200 includes plug 210 that connects tocircuit 100, which is contained in box 224 (an insulating container,such as, in some embodiments, a thermosetting plastic (e.g.,Bakelite™)). Plug 210 can be any of the many connectors used in variousoutlets (two or three conductors as needed by circuits 100-105 or 900),or can be simply probes. In some embodiments, light 212 (e.g., theoutput of LED 180 if FIG. 1B) goes on indicating the circuit is live.When momentary switch button 207 is pressed, switch 132 is closed, andthe timing circuit 130 is activated.

FIG. 2B is a perspective view of a socket-plug-type circuit breakerinterrupter/tester 201 embodying features of the present invention.Tester 201 is useful for testing circuit breakers that supply only lampoutlets, or for testing circuits that are inconvenient to test using awall outlet tester such as tester 200 of FIG. 2A. In some embodiments,connection 211 includes hot prong 172 and neutral prong 171 as alamp-socket plug at an end of box 225. Tester 201 can be screwed into alamp socket that is attached to a circuit breaker being tested, and insome embodiments, includes a light 212 that is on when the circuit haspower (i.e., after device 201 is plugged in but before it causes thecircuit breaker being tested to break. Optional activation switch button207 acts to activate control circuit 130. If button 207 is pressed andlight 212 does not go off, this indicates a failure of the instantaneousbreak function of the circuit breaker being tested.

In some embodiments that omit activation switch button 207, light 212will go on when tester 201 is initially plugged into an active circuit,then some short time thereafter (e.g., ten seconds, for example, assensed by a timer or a circuit that counts the number of cycles or zerocrossings of the AC line), controller 130 will activate electronicswitch 110, and light 212 should turn off, due to the opening of thecircuit breaker being tested. If the light does not turn off (after tenseconds, for example), this indicates a failure of the instantaneousbreak function of the circuit breaker being tested.

Unlike testers that introduce a permanent overload that lasts until thecircuit breaker trips (thus risking overheating of the wiring circuit320 (see below) and risking a fire if the circuit breaker does not tripas it is supposed to), a tester 201 (or tester 200) of the presentinvention will activate electronic switch 110 for only a partial halfcycle, a half cycle, or just a few half cycles or full cycles and thenwill turn off the electronic switch 110 (e.g., stop triggering it).

In some embodiments, the instantaneous circuit breaker tester 201includes one of the variations of circuit 103, 104, 105 or 900. This iselectrically the same as the instantaneous-trip testing portion ofcircuit 101 of FIG. 1B.

FIG. 3 is a block diagram that shows the relative positions of thedevice of this disclosure and the elements of the existing electricalsystem. FIG. 3 shows one device of the present invention 200 connectedto circuit 300 of breaker 338 of breaker panel 322 via circuit wires 320and outlet 326. Upon turning on device 200, the momentary current surgein the AC line 320 is sensed by that circuit's circuit breaker 338 andcauses it to unlatch. SCR 110 turns off at zero crossing so currentceases flowing. The circuit interrupter 338 continues its trippingaction to completion where upon current through the circuit 320 leadingto the outlet 326 and indicator light 212 goes out, indicating thatpoint in the circuit is no longer live, and tester 200 is no longerpowered.

FIG. 4 is a log-log graph of tripping time vs. current of an exemplaryor sample 90-amp circuit breaker. One aspect of instantaneous circuitinterrupters that is overlooked is that they are designed to respond(interrupt current flow) to a relatively high amplitude of the sine waveof AC power flowing through them, as opposed to the thermal element in acircuit interrupter that reacts to accumulated heat resulting fromrelatively long overcurrents of relatively low levels (low multiples ofthe rated current). Thus, it is unnecessary to impress both halves(i.e., positive going and negative going) of the sine wave upon theinstantaneous sensor to cause it to trip (even though the trip itselfmay occur later, for example, a single half cycle of high current cancause the trip to occur up to, e.g., three cycles later).

Utilizing half the sine wave will activate the tripping reaction andresult in less heat generated (in device 200, as well as in the wiringof the house circuit being tested) during the test, since the short isremoved, often before the trip has occurred. Even though many circuitbreakers have arc suppression features, the clearing time can be up tothree cycles (about 50 milliseconds) for many breakers, even though onlya single half-cycle (about 8.3 milliseconds) of high current issufficient to trigger the breaker to open. Tester devices that maintainthe short until the breaker actually opens can cause excess stress inthe breaker and the house wiring, since the short is maintained up tosix times a long as should be needed to trip the breaker, and evenlonger if the breaker is faulty and does not trip. Thus, someembodiments of the present invention maintain the short for only about ahalf cycle of the 60 Hz AC current (about 8.3 milliseconds), or evenless than a half cycle in some embodiments.

Additionally there is the apparent notion that a longer test (a longerduration of the short circuit) is better, while in actual fact, anefficient circuit interrupter will respond in less than the specifiedtrip timing parameters. This is because “instantaneous” is something ofa misnomer. As shown in FIG. 4, although the circuit interrupter'ssensing element may react and initiate tripping, for instance, duringthe first half cycle of the sine wave, the physical action of thetripped element moving from closed (shown in FIG. 4 by points A1, B1,and C1) to open (shown in FIG. 4 by points A2, B2, and C2) position maytake several cycles without requiring concomitant exposure to thetripping current. As described on page 12 of Cooper Bussmann BulletinEDP-2 Selective Coordination of Overcurrent Protective Devices for LowVoltage Systems, “Once a breaker unlatches, it will open. At theunlatching point, the process is irreversible.” From the samepublication on page 5, “ . . . the unlatching time indicates the pointat which the breaker senses an overcurrent in the instantaneous regionand releases the latch holding the contacts. However, the fault currentcontinues to flow through the breaker and the circuit to the point offault until the contacts can physically separate and extinguish the arc.Once the unlatching mechanism has sensed an overcurrent and unlatched,the circuit breaker will open.” Thus a longer testing period may notonly be unnecessary, but lead to both inaccuracies in analyzing theresults of the test and bring unnecessary stress on the interrupter, thetest device and the wiring circuit's components.

Thus, as used herein, “instantaneous-trip function” means a tripfunction that includes no intentional or substantial time delay such aswould be encountered in a thermal or overload-trip function. Aninstantaneous-trip function is typically triggered by an electromagneticforce, but could be sensed and triggered by a current sensor coupled toa microprocessor. An overload-trip function is typically triggered by athermal sensor such as a bi-metallic strip, but could also be sensed andtriggered by a current sensor coupled to a microprocessor that would nottrigger immediately, but would trigger if an overcurrent was maintainedfor a substantial number of cycles of the AC current being sensed.

In any case, a testing period that extends beyond the specified timingtrip parameters of the circuit interrupter will not be testing whetherthe interrupter is functioning within the manufacturer's specifications.

FIG. 5 graphically shows this principle in action. FIG. 5 is a graph 500showing several complete cycles (509 and 520) of AC electricity withnormal load current and current during an overload. The duration ofshort-circuit conduction is indicated by half cycle 510. At point A theovercurrent commences. Point B is the peak of the impressed current. Atpoint C the current ceases. Sometime between points A and C unlatchingis initiated. Sometime between points A and D, but subsequent tounlatching, the interrupter completes the tripping cycle. FIG. 5 showsthat it is possible to apply the high “short” current for much less timethan would be immediately apparent were one to judge by the totalclearing time (in some embodiments, the specified clearing time of acircuit breaker being tested is three full cycles, or about 50milliseconds).

Were the tester 101 to be turned on for the full three cycles, about sixtimes as much power would go into heat in the tester 101 and in thewiring between the circuit breaker and the tester 101. Thus, by notturning on the SCR 110 after the first half cycle, a safer test isprovided and less heat is generated. In other embodiments, theelectronic switch (either SCR 110 or a triac or power MOSFET that isused in place of SCR 110) is triggered to conduct for more than one halfcycle, but for less than or equal to the specified trip time of thecircuit breaker-under-test, in order to reduce the heat generated ascompared to a tester that conducted right up to the point that thecircuit breaker opened.

In yet other embodiments, tester 101 is programmed to provide a shortseries of pulses (perhaps five, ten or twenty pulses, (or, in otherembodiments, any suitably limited number of pulses) and thus anequivalent number of half cycles) that enable conduction by the shortingelectronic switch for a period of time longer than the specified triptime, but for a time much shorter than would reliably be provided by amanually operated switch closure. Thus, in most cases the conductionwould stop by the circuit breaker being tested opening. However, if thecircuit breaker did not trip in its specified time, or longer, thentester 101 would stop conduction of the shorting circuit well before afire or other catastrophe occurred. Even twenty pulses results in ashort that lasts for only one third of a second.

In some embodiments, point A where the tester starts conducting theshort-circuit current (as limited by resistor 120) is triggered at atime shortly after the zero crossing of the normal load current, inorder that the SCR is reliably and consistently triggered. In some suchembodiments, a time is selected approximately 0.5 millisecond(corresponding to about 20 volts) to 1 millisecond (corresponding toabout 40 volts) after the zero crossing, in order that the voltageacross the SCR is at least about 30 volts.

FIG. 6 shows a graph 600 of how the DC component of the 120VAC signal issometimes skewed relative to zero volts by a strong short-circuitcurrent. Dotted line 630 represents the rated load current, and thenominal zero crossing points Z, for a given circuit breaker. At timepoint 610, the SCR is turned on and a sharp current increase is seen,resulting in a DC shift of the subsequent current waveform. At timepoint 612, the normal zero crossing would have occurred, but for the DCskew that was added, and thus SCR 110 will not turn off until time point614, which is somewhat later, thus lengthening the time that the SCR 110conducts and increasing the power and heat generated. In someembodiments, a longer time delay is provided for the onset of conductionpoint 610, thus providing a smaller fraction of a half-cycle conductionperiod.

Cooper Bussmann Bulletin EDP-1 Part 1 A Simple Approach to Short CircuitCalculations states on page 3, “Short circuit current normally takes onan asymmetrical characteristic during the first few cycles of duration.That is, it is offset about the zero axis, as indicated in its FIG. 1(which corresponds to FIG. 6 in this document).” This initial heightenedamplitude can be taken advantage of by a tester that has a testingperiod of only a few cycles. FIG. 6 also graphically shows howimpressing the current of the first half of each sine wave's cycle willbe utilizing the highest amplitude halves of the sine waves in the caseof a short circuit. It is believed the same would be true of a highovercurrent situation, for instance, where 20- or 40-times the ratedcurrent is impressed.

Additionally, as the peak of the impressed current is the pertinentportion of the testing cycle insofar as activating the instantaneoustripping element, it becomes important to ensure that this peak is partof the testing period. One method of ensuring this is to have a timerthat operates relative to the actual cycles of the AC power sine wave.The device of the present invention does this.

Another overlooked aspect of testing instantaneous circuit interruptersis that they are designed to trip when the current is above a specifiedcurrent level. Thus creating a true short circuit is not necessary.

FIG. 4 shows examples of overcurrents of, among others, 20-, 30- and40-times the rating of the interrupter that results in unlatching timesof less than 0.007 seconds, which is less than ½ cycle of 60-Hz ACpower. A true short circuit can have undesirable side effects, forinstance, by placing unnecessary stress on the testing device switchingelement. Additionally, by impressing an unnecessarily high current flowupon the interrupter the test will not indicate if the interrupter isoperating within actual specified parameters.

An optimum test of the circuit interrupter is one that minimizes theexposure of the interrupter, its circuit and the testing device to highcurrents while performing a test that will accurately reflect thespecified parameters of the instantaneous circuit interrupter.

The device of the present invention meets these testing requirements bypresenting a tester that includes a timer which is activated bothrelative to the zero-cross of the sine wave and is on for periodsrelative to actual cycles of AC power, optionally being on only duringone half of that AC power's sine wave. It also includes means forlimiting the amplitude of the current peak.

A further embodiment of the present invention includes a circuit forlimiting the on time of the testing period to specified time lengthsrelative to AC sine wave cycles. Circuits for timing electronic circuitsrelative to AC sine wave cycles are well known, as, for example, indigital clocks that use the AC sine wave as a clocking source. In thecase of the device of the present invention such a timing method can beused to limit the test's timing length to multiples of AC sine wavescounted by the tester's timing circuit as charted in FIG. 5.

FIG. 7 is a log-log graph 700 of tripping time in seconds versesmultiples of current rating of a circuit breaker. FIG. 8 is a log-loggraph 800 of tripping time in seconds verses multiples of currentrating. These are discussed further below.

Referring now to FIG. 9, the timing circuit is considered as a whole bynumeral 130. Timing circuit 130 controls switching transistors Q1 andQ2, which in turn control the larger SCR 110 which is in series withload 120. In other words, the output of the timing circuit 130 turns onNPN transistor Q1, which turns on PNP transistor Q2 which in turntriggers SCR 110 via the resistor R5 and resistor R9 gating circuit. Themomentary current surge is limited by the resistance load 120.

In some embodiments, control circuit 130 includes a programmablemicrocontroller U1 (such as a PIC12C508 microcontroller from MicrochipTechnology Incorporated of Chandler Ariz.) programmed to receive astimulation indication from switch 132 (formed of SW1 and R10), and toreceive a zero crossing indication from R8 and C6. Optional switch SW3(with R11 and R12) encodes a cycle-selection indication, allowing theuser to select a number of pulses to be generated. In some embodiments,controller U1 provides an active-low drive signal for LED D5 connectedto R13, turning on the LED when the circuit is ready to be triggered.The LED turns off once the circuit breaker being tested opens.Controller U1 outputs one or more gate pulses from its pin 5, drivingNPN transistor Q1 through R7. When Q1 turns on, it pulls the base of PNPtransistor Q2 low (via resistors R4 and R6), turning it on, andproviding an output pulse to SW2 of almost 5 volts (less the saturationvoltage of Q2). Switch SW2 is selectable to activate SCR 110 (throughresistor divider R5 and R9, where R9 normally keeps SCR 110 turned off)or triac 150 (through resistor divider R14 and R18, where R18 normallykeeps triac 150 turned off).

The operation of circuit 900 of FIG. 9 is otherwise as described forcircuit 101 of FIG. 1B.

To assist a person skilled in the art of electronics, a somewhatdetailed specification of power supply 140 is offered herewith: 120-VACline voltage is converted to five volts DC in the power supply 140. Thepower supply converts the high voltage to 5 volts by transferring thecharge from a small capacitor (C1) to a larger one (C5 and C7 and C4)via diodes D1, D2 and D3. This type of power supply doesn't need adropping resistor or transformer. In the power supply, a resistor (R8)drops the AC voltage to a safe level for input to a microcontroller todetect when the AC line crosses zero volts. In some embodiments, theprotective diodes on the inputs of the microcontroller prevent thevoltage from going above or below the power supply rails.

When the push button (SW1) is pressed, the microcontroller (U1) firmwarewaits for a low to high zero crossing then, after a short delay, outputsa pulse to fire either SCR 110 or triac 150, based on the position ofswitch 136. The short delay allows time for the AC line to reach avoltage high enough (e.g., approximately 30 volts, in some embodiments)so the SCR (thyristor) 110 can reach its holding current. This processis repeated on the high to low zero crossing to provide a second pulsein the second half of the first cycle, so the triac can fire on bothhalves of the AC cycle, although the SCR essentially ignores the secondpulse since it is a uni-direction switch. In some embodiments,controller 130 provides three pulses in three consecutive half cycles,wherein triac 150 conducts during all three half cycles (anegative-going, a positive-going, and a negative-going half cycle) ifswitch 136 is in the GFCI-testing position, and SCR 110 conducts onlyduring the middle half cycle (the positive-going half cycle) triggeredby the second of the three pulses, since it conducts only for thepositive half of the cycle.

Note: The internal common is connected to the hot wire of the 120-voltAC line, so the positive half cycle as seen by SCR 110 is when the inputHOT line is negative relative to the neutral line.

Note: Optional switch SW4 is provided to connect the neutral and groundwires together at the tester, thus halving the resistance that isotherwise provided by the neutral wire alone, thus lowering theresistance of the overall circuit and reducing heat in those wires.

When the switch is in the triac position, the current from the triggerpulse is directed to the triac gate. The triac latches on because thecurrent through R17 is above the holding current. R17 provides the testcurrent for a GFCI breaker. For a single AC cycle current flows from hotto safety ground, which should trip a good breaker.

When the switch is in the SCR (circuit-breaker-test) position, thecurrent from the trigger pulse is directed to the SCR gate. The SCRlatches on for one-half cycle of the AC line, driving current betweenhot and neutral through the load. Since SCRs can only conduct in onedirection, the high to low zero crossing pulse does not fire the SCR.The load is a small enough resistance so the current between hot andneutral will trip a good circuit breaker.

Multiple numbers of trigger pulses can be selected with selector switch(SW3). Obviously, the microcontroller can be programmed for variationsof numbers of pulses and placement of pulses at desired points in thesine wave relative to the zero crossing.

FIG. 10 is a wiring diagram of a tester device circuit 1000 of anotherembodiment of the device. Dotted block 1152 indicates the switch andgating elements. Dotted block 1150 indicates the power supply and timingcircuit. Dotted block 132 indicates the two series-connected activationswitches. The rest of the circuit is explained below.

FIG. 11 is a circuit diagram 1100 of the device of FIG. 10. In someembodiments, the plug 210 includes neutral prong 5 a and hot prong 5 b,as well as button 1149 that closes switch 1148 when it is pressed by theact of plugging device 1100 into an outlet. The circuit components andvalues used for some embodiments are set forth below.

For example, for household circuit breakers that are 120-volts AC and 20amps or less, the following values will provide a very durable setup,used for some embodiments. Two prong plug 210 suitable for standard120-volts AC outlet, a neon light 1112 with appropriate series resistor,momentary switch 1114 (used to activate the test function), SCR 110rated for 200-volts AC/65 amps, 0.1-mF capacitor 1128, 32-volt diac1130, 200-volt, 1-amp diode 1132, 10K-ohm ½-watt resistor 1134, 0.15-ohm50-watt resistor 120. A 0.1-mF capacitor 1142 and a 100-ohm ½-wattresistor 1144 form a “snubber” that can aid in protecting the SCR byabsorbing momentary current surges during shutoff orconnecting/disconnecting to the circuit 300 (see FIG. 3). Means, such asa heat sink, are, in some embodiments, provided to conduct away anddissipate heat from the SCR 110 and load resistor 120. Wires in device1100 that are carrying the high amperage current are a gauge sufficientto carry the current the particular circuit breaker will require totrip.

There are various possibilities with regard to the resistance andwattage of load 120 that can be varied depending on the limitations ofthe chosen switching element and the amplitude and duration of thecurrent tripping requirements of and the current supply to the circuitbreaker in question. Note that the resistor load may be eliminateddepending on the current limitations of the switching element.

Although the circuit of FIG. 11 is considered to be one embodiment,other alternate embodiments are possible. In particular theseembodiments envision different timing circuits, switching devices,gating or on/off circuits and incorporated safety features.

It will be understood that although an SCR 1110 is shown as theswitching device in electronic switch 110, that is, an SCR 1110 has beenshown in the circuit to perform a switching function, other alternativeswitching devices, such as an MCT (MOS-controlled thyristor), a triac, apower MOSFET, or other high-current semiconductor device could be used,with appropriate gating circuits or physical control mechanisms. Suchswitching elements can be paralleled to carry higher currents.

FIG. 11 also shows momentary switch 1148 (a switch that is activatedwhen tester is inserted into its receptacle) in series with switch 1114(which is manually activated to initiate the test). Switch 1148 helpsprevent accidental activation (e.g., if switch 1114 is depressed whileinserting the tester into an outlet) and prevent arcing between the plugand the outlet by not allowing turn on until the plug is completelyseated (which then closes switch 1148). This arcing could occur in theabsence of switch 1148 if the user held momentary switch 1114 closed asthe device was inserted into the receptacle. It will be understood bythose skilled in the art that this feature could be located elsewhere inthe circuit of the device. This is illustrated in FIG. 11 with switchbutton 1149 (which closes switch 1148) located between the terminals ofplug 210.

In some embodiments, controller circuit 130 includes a CMOS latch pair1109 of type CD4013BCN, wired as shown with capacitor 1101 connectedbetween output not-Q1 and ground, that, when activated by the closing ofboth switch 1148 and switch 1114 (connected to resistor 1102 andcapacitor 1103 which are also connected to the internal signal groundVss), produces a single pulse through capacitor 1104 to activate smallSCR 1118, through RC pair 1134 and 1128, diode 1132, and DIAC 1130 thenactivates SCR 1110 to turn on a half-cycle current pulse limited by loadresistor 120.

Resistors 1108 and 1107, diodes 1105 and 1106, and capacitor 1110 formpower supply 140.

In some embodiments, a neon light 1112 (with appropriate internallimiting resistor) indicates when power is on power contacts 5 a and 5b; and neon light 1113 (with appropriate internal limiting resistor)indicates when power is on internally (i.e., when external power isapplied power contacts 5 a and 5 b and resistor/fuse 120 is not open(the fuse blown).

Further, the load resistor 120 can act as a fuse in addition to, or inplace of, fusible link 1154 in order to provide protection in the eventthe circuit breaker 338 (FIG. 3) does not function correctly. As this isa cascade arrangement of circuit protection, there will have to be acoordination between load resistor 120 fusible link 1154 and breaker338. In other words, the rating of the fusible link within the device ofthis disclosure should be such that it will not open before circuitbreaker 338 but such that it will open before the existing circuit orthe device of this disclosure can be damaged. It will be understood bythose skilled in the art that this feature could be located elsewhere inthe circuit of the device.

There are many standard variations on this circuit. For instance, thereare many different circuits of components for gating semiconductors thatare commonly known to those skilled in the art of electronics.Additionally, the microcontroller of the preferred embodiment of thisdisclosure provides a delay after connection to power to allow the plugto be fully seated before use and a delay after cycling the test toallow device components time to cool and to protect the circuitinterrupter and its associated circuit components. Such a circuit couldprovide a brief delay before allowing activation of the circuit,substituting for momentary switch 1148 that was described earlier inthis disclosure. In fact, in some embodiments with such a delay, bothswitches 1114 and 1148 are eliminated, and the microcontroller isprogrammed with many variations of delays, including one where thedevice would be plugged in and then function automatically after thedelay interval. Also, the microcontroller can be programmed to deliver apattern of gating pulses, for instance, a single pulse, followed by adelay and then another pulse.

The disadvantage of using a mechanical switch is that its contacts aresubject to wear, fusing, pitting and the action of a mechanical switchis necessarily slower and less accurate as compared with a solid stateswitching element. As the switching time of a semiconductor can be veryexactly controlled, the preferred embodiment of this device is with asemiconductor circuit as the “switch.” As there are many differentsemi-conductors available, again the choice of which to use is aquestion of current requirements and cost.

Although the preferred embodiment includes an on-time of one half cycleof AC power, it is understood that other lengths of on-time can beutilized. It is especially emphasized that by using the AC sine wave asa clock signal, as shown in FIG. 5, a timer can be set to be on forinteger multiples of the AC sine wave, or for ½ multiples of the sinewave, or for other predetermined time lengths. Since circuit breakershave different ratings, one can then set the tester to lengths of timemeaningful relative to the specifications of a specific circuit breaker.

Additionally, by measuring the amperage of the initial cycle ofoperation, one can deduce the impedance of the circuit of the circuitbreaker. If the impedance is large enough (i.e., the amperage of theinitial test is small enough), the resistance element of the tester canbe switched out of the circuit and a subsequent test can be performedutilizing just the resistance of the circuit of the circuit breaker. Itis also possible to have multiple resistance elements that the usercould choose between to enable tests of different resulting amperage.These variations are well known to those knowledgeable in the art.

Also, it is a simple adaptation to have the resistance connect betweenthe hot and ground wires to test other kinds of circuit breakers, suchas a ground fault interrupter, by use of a suitably sized resistance andlength of on-time. This is shown in FIG. 9 where the triac connects hotto ground via resistor R17. Thus the device of this disclosure can beused to test multiple types of circuit interrupters. It is also possibleto selectively test breakers by selecting which outlet wires to test. Inother words, given a circuit with multiple breakers arranged in acascade arrangement, one can test only a panel's circuit breaker, oronly a ground fault interrupter (which could be, for instance,downstream from the panel's breaker as shown in FIG. 3), leaving theother breaker still in an on position or setting. The tester could havetwo buttons, one for each type of breaker test, or a switch to choosebetween the various tests.

Additionally, there are numerous circuit finders in existence thatutilize a transmitter plugged into an outlet and a receiver or sensor atthe circuit breaker panel. An electrical circuit finder has atransmitter that is plugged into one of the circuits of a building'selectrical system and a receiver that is used to identify other elementsof the circuit such as a circuit breaker, fuse, switch, electricaldevice or outlet. By combining a circuit finder with the circuit tester(the device of the present disclosure) one could first test the circuitbreaker and, if the breaker were in working order, it would trip. If thebreaker did not trip, then one could use the circuit finder to determinewhich breaker to turn off manually.

Also, a noise maker, such as a piezo buzzer, could be incorporated intothe device of this disclosure to allow locating an outlet by the oldmethod of flipping breakers off until the noise stops.

Also, although the device of this disclosure utilizes an LED to indicatethat the circuit is live, it will be obvious that other indicators, suchas a neon light, buzzer or vibrator could be included to do this.

Operation

FIG. 12 is a flow chart 1200 of the operation of some embodiments of theinvention. At block 1210, the tester is connected to the circuit beingtested (e.g., a household wiring circuit 300 protected by a circuitinterrupter 338. In some embodiments, the circuit-interrupter includesan overload-trip function and an instantaneous-trip function. In someembodiments, a signal (such as a small light indicator or a soundindicator (e.g., a beeper or a voice synthesizer) is output thatindicates the tester is ready to perform the test. At block 1220, thetester receives a stimulation indication (for example, a user presses a“test” button, or a timer pulse is received after a predetermined amountof time after the tester is connected). At block 1230, the testerselectively connects an electrical load to wires connected to thecircuit interrupter based on the reception of the stimulationindication, wherein the electrical load is sufficient to trigger theinstantaneous-trip function of the circuit-interrupter. In someembodiments, a signal (or lack thereof), such as a light or beeperturning off or a voice synthesizer that indicates failure due to thepower still being applied, indicates the success or failure of thecircuit breaker to trip as specified.

In some embodiments of the method, the selectively connecting (block1230) includes connecting the electrical load to the circuit-interrupterfor a time no greater than a pre-specified maximum trip time of theinstantaneous-trip function. In some embodiments of the method, thepre-specified maximum trip time of the instantaneous-trip function isthree cycles of AC power. In some embodiments of the method, theselectively connecting includes connecting the electrical load to thecircuit-interrupter for a time no greater than about one-half cycle ofAC power. In some embodiments of the method, the selectively connectingincludes providing an enabling control signal pulse to an SCR at a pointin time (e.g., delayed slightly from the zero-crossing of the AC signal)when an electrical load on the electronic switch is at least about 30volts.

Some embodiments of the method further include stopping electricalconduction (block 1240) in the electrical load as a result of a failureof the selectively connecting to stop conduction.

The operation of one embodiment of the device of this disclosure permitsthe user to: (1) determine if the outlet is live, (2) to turn off thepower to that outlet, and (3) to see that the power is off, all from thelocation where the user wishes to work.

A compact housing a few inches in each dimension is simply plugged intothe outlet. A light indicates if the power is on. Depressing a buttonallows a brief surge of current that causes the circuit interrupter totrip off. The light turns off indicating the power is now off. In someembodiments, all of this is done at the outlet to be worked on.

If the circuit breaker is faulty and will not flip to the off position,the indicator light will show the circuit is still live.

The current surge has a duration of only a fraction of a second and theamplitude of the current surge is limited. This means that minimalstress is presented to the device, the outlet, the wiring in the circuitand the circuit breaker of the circuit.

Further, with minor modifications (for example, different plug shapesfor different style outlets or simply probes connected to circuit 900 ofFIG. 9), it can be adapted for use in a wide variety of situationsincluding standard receptacles (see FIG. 2A), light bulb receptacles(see FIG. 2B) or bare wires (see FIG. 9). Similarly, the device can beconstructed to be used with a variety of voltages and currents.

In order to design and build an optimum circuit breaker locator, it isnecessary to give a brief explanation of the mechanism and operation ofcircuit breakers and fuses.

Fuses and breakers operate in fundamentally different manners in thecase of short circuits. Fuses are thermal devices. When there is a shortcircuit an element in the fuse heats up and melts. However, in the caseof a short circuit a circuit breaker senses a magnetic wave that exceedssome threshold value (i.e., caused by the excess current of the shortcircuit). This wave causes the breaker to trip. Referring now to FIG. 5,one sees that a fuse is designed to blow early in the first half cycleof the AC surge, as illustrated by line AE, while a circuit breakertakes between one-half and three cycles to trip, as illustrated by linesAB and AD. Thus the fuse would usually blow before the circuit breakereven initiates its tripping cycle.

In experiments with a prototype of the device of this disclosure, it hasbeen found that a large current surge of a half cycle of AC issufficient to cause a circuit breaker to trip, although the mechanical,physical action may take longer. The desirable aspect of this is thatthe shorter the duration of the current surge, proportionately less heatis created.

Referring now to FIG. 7, one sees a log-log graph wherein the amperageof the load, overload or short circuit is compared with the circuitbreaker's clearing time, or the time it takes to trip. The vertical axisis the clearing time in seconds, and the horizontal axis is the multipleof the current rating of the circuit breaker. For example, if there is a40-ampere load on a 20-ampere circuit breaker, the multiple of currentrating would be two and the clearing time would be between approximately15 and 100 seconds.

If one is dealing with a 15-ampere breaker in a panel that is in turnprotected by a 100-ampere breaker, with a 600-ampere current, the15-ampere breaker will experience a forty times its current ratingcurrent and trip nearly instantaneously, while the 100-ampere breakerwill have only a six times current rating multiple current and not tripfor between approximately 0.8 and 6 seconds. Thus, one can trip thesingle 15-ampere breaker and not the 100-ampere breaker which are in aseries relationship.

Molded case circuit breakers (MCBs) with both thermal and magnetic tripsaccount for 90-95% of circuit breakers presently in use, and for atleast 80% of those now being specified. As the name implies, athermal-magnetic trip unit has two separate overcurrent tripping devicesor elements. One is a bimetallic thermal element, that responds to theheating effect of the current through the MCB. This element establishesthe continuous current rating and provides time-delay overcurrentprotection up to ten times breaker continuous rating. The other trippingdevice is an “instantaneous” magnetic element that responds to themagnetic field produced by current through the MCB. It is basically asolenoid, which unlatches “instantly” once current exceeds pick-up(trip) setting.

In smaller breakers, the instantaneous trip unit pick-up setting isfixed, usually at ten times continuous current rating.

The time-current characteristics for typical 100-amp MCB are shown inFIG. 8. Other amperage breaker's ratings are similar.

Note that the time-current characteristics are shown as a band. Thisindicates the minimum and maximum tripping time resulting from breakermanufacturing tolerances. Values of time-current to the left of the bandshould not cause the breaker to open. Values of time-current to theright of the band should always cause the breaker to open. While valuesthat fall within the band may or may not open the breaker.

Note the part of the band labeled instantaneous trip. The pick-upsetting is approximately 1000 amperes that lies in the center of theband. Since this portion of the band is vertical, it indicates that thetrip element will unlatch the breaker for any value of current thatexceeds the maximum tolerance, and may unlatch it for any value ofcurrent that exceeds the minimum tolerance. The unlatching time isextremely fast. In some cases as little as 0.0001 seconds.

However, the breaker does not clear the circuit that fast. It requirestime for the parts to move after the breaker is unlatched. The openingor clearing time is indicated by the horizontal (or nearly horizontalportion of the curve. The total clearing times for thermal-magnetic MCBrange from about ¾ cycle for very small MCB to about two cycles or morefor the largest MCB.” [From Littlefuse Basic Terminology pg 77 & 79]

There is little advantage in generating an amperage greater than fortytimes the current rating of the breaker insofar as shortening theclearing time. This is especially clear as shown in FIG. 4.

By generating a limited high peak current of limited duration one candesign and build an optimum instantaneous circuit interrupter testingdevice. There are many well known means, including, but not limited to,microcontrollers, one-shot timing circuits, flashers and sequentialtimers, for limiting the on-time and delay before or after usage.

Aside from the timing means utilized, the designer must take intoaccount:

a. the current rating of the breakers to be tripped that will determinethe amplitude of current desired;

b. the duration of current required;

c. the SOA (safe operating area) of the chosen switching elementconcerning current amplitude and duration of said current;

d. the electrical current supply available; and

e. the cost of parts.

Of these, there are two main limitations the designer must take intoaccount. First, each switching element has limitations as to the peakcurrent it can safely switch for a given duration of time, commonlyknown as the safe operating area or SOA. Second, the cost of parts andtheir associated gating elements. In the case of the preferredembodiment of the present invention, an SCR has been used forinstantaneously tripping a circuit breaker as SCRs are generallyrelatively inexpensive for the overcurrent levels they can switchreliably. Additionally, an SCR conducts for only one half of the AC sinewave, incurring less stress on the device and the components of thecircuit to be tested.

In some embodiments, a small triac is used for the GFCI-testing portionof the device because it can conduct on both halves of the AC sine wave.The small currents generated in the test present no heating problems sothere is no additional stress to any components.

The present invention provides a simple and effective way to test theinstantaneous-trip function of a circuit-interrupter. One aspect of theinvention provides a tester for a circuit-interrupter, wherein thecircuit-interrupter includes an overload-trip function and aninstantaneous-trip function. This tester includes an electrical plughaving a first external electrical connector and a second externalelectrical connector, a control circuit that outputs a control signal,an electronic switch selectively enabled by the control signal, and anelectrical load connected to the electronic switch such that theelectronic switch connects the electrical load to the first externalelectrical connector and the second external electrical connector ascontrolled by the control signal, wherein the electrical load issufficient to trigger the instantaneous-trip function of thecircuit-interrupter.

In some embodiments, the circuit-interrupter has both an overload-tripfunction and an instantaneous-trip function, and the tester trips onlythe instantaneous-trip function.

In some embodiments of the tester, the control signal enables theelectronic switch to conduct limited to a time no greater than apre-specified maximum trip time of the instantaneous-trip function.

In some embodiments, the pre-specified maximum trip time of theinstantaneous-trip function is three cycles of AC power. In some suchembodiments, the electronic switch is enabled to conduct for a time nogreater than about one-half cycle of AC power.

In some embodiments of the tester (whether or not the maximum trip timeis specified as three cycles), the electronic switch is enabled toconduct for a time no greater than about one-half cycle of AC power.

In some embodiments, the electrical load acts as a fuse that opens as aresult of failure of the electronic switch to stop conduction.

In some embodiments, the electronic switch includes a silicon-controlledrectifier (SCR), and the control circuit provides an enabling controlsignal pulse to the SCR at a point in time when an electrical load onthe SCR is about 30 volts. In some such embodiments, the electronicswitch is enabled to conduct for a time no greater than about one-halfcycle of AC power.

In some embodiments, the control circuit includes a programmablecontroller.

Some embodiments further include a ground fault tester circuit thatcomprises a small current load selectively coupled between the firstexternal electrical connector of the plug and a third externalelectrical connector of the plug.

Some embodiments further include a manually activated switch coupled tothe control circuit, wherein the switch initiates output of the controlsignal.

Another aspect of the present invention provides a method of testing acircuit-interrupter, wherein the circuit-interrupter includes anoverload-trip function and an instantaneous-trip function. This methodincludes receiving a stimulation indication, and selectively connectingan electrical load to wires connected to the circuit interrupter basedon the reception of the stimulation indication, wherein the electricalload is sufficient to trigger the instantaneous-trip function of thecircuit-interrupter.

In some embodiments of the method, the selectively connecting includesconnecting the electrical load to the circuit-interrupter for a time nogreater than a pre-specified maximum trip time of the instantaneous-tripfunction.

In some embodiments of the method, the pre-specified maximum trip timeof the instantaneous-trip function is three cycles of AC power.

In some embodiments of the method, the selectively connecting includesconnecting the electrical load to the circuit-interrupter for a time nogreater than about one-half cycle of AC power.

Some embodiments of the method further include stopping electricalconduction in the electrical load as a result of a failure of theselectively connecting to stop conduction.

In some embodiments of the method, the selectively connecting includesproviding an enabling control signal pulse to an SCR at a point in timewhen an electrical load on the SCR is about 30 volts.

Yet another aspect of the present invention provides a tester for acircuit-interrupter, wherein the circuit-interrupter includes anoverload-trip function and an instantaneous-trip function. This testerincludes an electrical plug having a first external electrical connectorand a second external electrical connector, and means as describedherein for selectively connecting an electrical load to the firstexternal electrical connector and the second external electricalconnector, both being connected to the circuit interrupter, wherein theelectrical load is sufficient to trigger the instantaneous-trip functionof the circuit-interrupter. In some embodiments of this tester, thecircuit-interrupter has both an overload-trip function and aninstantaneous-trip function, and the tester trips only theinstantaneous-trip function.

In some embodiments of such a tester, the means for selectivelyconnecting includes means for connecting the electrical load to thecircuit-interrupter for a time no greater than a pre-specified maximumtrip time of the instantaneous-trip function. In some embodiments ofsuch a tester, the pre-specified maximum trip time of theinstantaneous-trip function is about three cycles of AC power, and theelectronic switch is enabled to conduct for a time no greater than aboutone-half cycle of AC power.

Still another aspect of the invention provides a tester for acircuit-interrupter. This tester includes an electrical connectionhaving a first external electrical connector and a second externalelectrical connector, a control circuit that outputs a control signal,and a first electronic switch selectively enabled by the control signalsuch that the electronic switch conducts an overcurrent between thefirst external electrical connector and the second external electricalconnector and then stops conducting at a point in time before thecircuit-interrupter opens its circuit.

In some embodiments of this tester, the circuit-interrupter includes aninstantaneous-trip function, and wherein the electronic switch conductsan overcurrent between the first external electrical connector and thesecond external electrical connector and then stops conducting at apoint in time before the instantaneous-trip function of thecircuit-interrupter opens its circuit. In some such embodiments, thecircuit-interrupter also includes an overload-trip function, and thetester trips the instantaneous-trip function of the circuit-interrupterbut not the overload-trip function of the circuit-interrupter.

In some embodiments of this tester, the electronic switch is enabled toconduct for a time no greater than about one-half cycle of AC power.

In some embodiments of this tester, the electronic switch includes asilicon-controlled rectifier (SCR), and the control circuit provides anenabling control signal pulse to the SCR at a point in time after azero-crossing.

Some embodiments of this tester further include a ground fault testercircuit that comprises a small current load selectively coupled betweenthe first external electrical connector of the plug and a third externalelectrical connector of the electrical connection.

In some embodiments of this tester, the overcurrent is limited by aresistance in the tester of about 0.15 ohms.

It is understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. An apparatus for testing a circuit-interrupter, wherein thecircuit-interrupter includes an overload-trip function and aninstantaneous-trip function, the apparatus comprising: an electricalplug having a first external electrical connector configured forline-conductor connection and a second external electrical connectorconfigured for neutral-conductor connection; a manually activatedelectronic switch; and an electrical load operatively connected to theelectronic switch such that the electronic switch connects theelectrical load to the first external electrical connector and thesecond external electrical connector momentarily, wherein the electricalload is sufficient to trigger the rated instantaneous-trip function ofthe circuit-interrupter, and wherein the electronic switch automaticallydisconnects the electrical load in about 1/20 second or less whether ornot the circuit interrupter trips.
 2. The apparatus of claim 1, whereinthe control signal enables the electronic switch to conduct limited to atime no greater than a pre-specified maximum trip time of theinstantaneous-trip function.
 3. The apparatus of claim 2, wherein thepre-specified maximum trip time of the instantaneous-trip function isthree cycles of AC power.
 4. The apparatus of claim 3, wherein theelectronic switch is enabled to conduct for a time no greater than aboutone-half cycle of AC power.
 5. The apparatus of claim 1, wherein theelectronic switch is enabled to conduct for a time no greater than aboutone-half cycle of AC power.
 6. The apparatus of claim 1, wherein theelectrical load acts as a fuse that opens as a result of failure of theelectronic switch to stop conduction.